The present invention relates to the oil and gas industry. The Abrasive Hydrojet Perforation Technology offers an effective means to communicate the wellbore with the target formation and to achieve more effective completion due to an increase of flow area, bypassing the damage in a near-wellbore zone and reduction of the compressive stresses The invention represents a new method of treatment of a near-well zone of the producing formation with a combination of chemical treatment.
It is known that flow from productive zones can be increased by slotting and chemical treatment. Slotting allows redistribution of the mechanical stresses in the near well zone, while chemical treatment allows increased productivity of the wells. However, the first method is very labor consuming and requires high costs. In order to shot three feet of the productive interval some time it is necessary to spend up to three hours of pumping unit operation, which is an expensive operation. The chemical action also treats the near well zone, but it requires a primary opening of the formation and does not remove a zone of support pressure which is a main reason of locking of the passages for fluid flow into the well. The first method is very efficient and increases the productivity of wells on average several times, however it is expensive. In order to provide maximum effectiveness or completely restore the potential productivity of wells, it is usually necessary to provide a subsequent treatment with formation-treating reagents.
Some of known solutions are disclosed for example in U.S. Pat. No. 3,965,982; patent document WO94/05898; SU 10472234; SU 1031263; SU 1167925; xe2x80x9cMethod Recommendations for Increase of Permeability of near Well Zone by slot Looseningxe2x80x9d by Ministry of Geology USSR, PTO xe2x80x9cSEIMORGEOLOGIAxe2x80x9d, L., 1984; I. N. Ivanov, et al xe2x80x9cFlow-in of Fluid to Well with the Use of Various Methods of Opening of Productive Formationsxe2x80x9d, Geophysical Magazine, 1984, no. 5; V. A. Sidorovski xe2x80x9cOpening of Formations and Increase of Productivity of Welsxe2x80x9d, M., Ndera, 1978, P111; xe2x80x9cMethod of Recommendations of Increase of Permeability of near Well Zone with Slot Looseningxe2x80x9d, Nii Geology Arctics, Mingeologii USSR, L. 1979.
The method disclosed in SU1167925 is the closest to the present invention. It is a combined method for the increase of productivity, which includes slotting of the well and cyclic acid formation treatment. The slotting is performed in accordance with known xe2x80x9cclassicxe2x80x9d recommendations in order to obtain a maximum possible effect, while the cyclic acid treatment is performed also in accordance with the known method described in the above mentioned documents, for a depth which is not less than 5 diameters of the well, so as to attempt to completely use its possibilities without the consideration of the results of slotting or control of the results of each cycle. The cyclical xe2x80x9cperiodicxe2x80x9d treatment of a well was performed by a reagent solution whose volume was determined from a mass and porosity of rock adjoining a shaft of the well, at a distance of approximately two diameters from the well. Each cycle of treatment is performed by pressing of a calculated volume of solution into the formation to be treated, which is preliminarily limited from above and from below by packers. The treatment in some sense is performed blindly, the results were evaluated in accordance with a change of productivity of the well. The cycles of treatment continued until the time when repetition did not lead to a change in productivity.
It has been shown from practice that this method which includes a complete slotting with a subsequent complete treatment with technological reagents has a universal action on the formation and provides an increase of well productivity, an equalization of a profile of advancement of a front of water pumped into a formation for maintaining of the formation pressure, an increase of the oil yield of the formation. Because of these advantages this method has been widely utilized. It also has been used during exploration and drilling of new wells. Moreover, it was made possible with this method to explore and efficiently use wells in low-production formations of Western Siberia in which the oil flow is less than 30 bbl per day. This method therefore is efficient. However, this method, similarly to the other methods has a limitation as to its possibility and efficiency. It is expensive, labor consuming and does not guarantee obtaining of the maximum possible increase of well productivity. The method is used without consideration of negative action of elevated stress concentrations, which are formed near the wellbore.
It is known that the maximum stresses in the near well zone are generated within one diameter of the well or approximately 0.6 ft., and the maximum stress directly adjoins the walls of the well (FIG. 1). The plastic zone in this case can be not considered, since in accordance with the calculation its width at the depth of 10,000 ft. is only 0.03 ft. It is also known that during the process of the drilling of wells, even after carrying out slotting, a zone of support pressure remains near it. The slotting removes only a part of these stresses, which is equivalent to a reduction of depth of the well approximately 1.5 times. During slotting at the depth of 10,000 ft. it is equivalent to a reduction of stresses to the depth of 6,600 ft. However, the mode and parameters of acid treatment (or treatment with other reagents, such as technological compositions) nowadays are determined without consideration of negative influence of the remaining stresses near the well. The zone of support pressure, which remains around the well, is not taken into consideration and parameters of treatment with technological compositions are calculated from the condition of action of a uniform supply of active technological solution per volume unit of a formation.
However, experimental observations and analytical investigations showed that the influence of zone of support pressure near the well is significant. If this influence is not taken into consideration, false conclusions can be made with respect to the productivity of the wells. Based on the results of the treatment, it is considered that a low oil yield from a formation can be explained by a week natural permeability of the formation itself, while a real cause is the reduction of permeability only within limits of the zone of support stresses, caused by stress concentration beyond the wellbore.
Accordingly, it is an objective of the present invention to reduce labor consumption and cost of treatment of a well, without a reduction of efficiency of treatment, time of use of wells, and gas/oil yield of productive formations.
In keeping with these objectives and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a method for increasing production of oil, gas and hydrogeological wells, which includes Abrasive Hydrojet Perforation Technology (AHPT) and a cyclical treatment of a near well zone with a formation treating reagent, with cutting of slots, determination of a productive zone, and a corresponding volume of a treating technological composition, and introduction (pressing through) of the volume into a formation to be treated, in which in accordance with the present invention the method is performed in two stages so that in the beginning a partial Abrasive Hydrojet Perforation of a near wellbore zone is performed so as to redistribute stresses, and then a remaining part of the support stresses is removed by a cyclical treatment of a well with a formation treating reagent with its control in accordance with the density of the formation to be treated and with a corresponding correction.
The following is a short summary of the benefits, improvements and the most promising applications of Abrasive Hydrojet Perforation technology:
The Abarsive Hydrojet Perforation Technology (AHPT) slotting provides a very precise, reliable and controllable method to establish a large inflow path between the cased borehole and the formation. The inflow area of an 8-in per foot dual slot is equivalent to 36 spf of 0.75-in shaped charge holes. Moreover, the pressure drop on AHPT slot is significantly less then on the areal equivalent set of perforated holes. In addition, the AHPT cutting process is much more robust in creating a low-resistant flow path, even with two strings of casing
AHPT slotting preserves the integrity of the cement bond. This can be critical for zonal isolation when the perforated intervals are in close proximity to water or a gas cap. The integrity of the cement sheath also increases the casing strength and resistance to failure.
The created AHPT slots simplifies the fracture initiation and therefore may significantly reduce the near wellbore problems (multiple fracturing, tortuosity, etc.). This reduces the chances of NWB screenouts during fracture stimulation and minimizes the choking non-darcy effect because of the tortuous path during production (esp., in gas wells).
AHPT slot geometry (with the penetration depth up to 4-10 ft) bypasses the near wellbore mud invasion zone and increases the drainage area. This suggests that AHPT slotting in clean, high permeability sands is the preferred completion method. If these clean formations require sand control, AHPT slotting can be used in combination with high rate water packs. For laminated formations, AHPT slots in combination with FandP should result in consistent negative skin completions.
AHPT cutting does not reduce the near wellbore strength of the formation, as does conventional shape charge perforating. Under some circumstances, this AHPT feature in combination with a larger created drainage area may allow a natural completion of formations that currently require sand control.
The slots modify the stresses in near the wellbore zone (relaxed in zone adjacent to the slots, and increased at the tip zone). Formations with strong stress-dependant permeability may encounters significantly reduced completion skin. Moreover, for deep and relatively hard formations. slotting may achieve compressive fracturing in the near wellbore region that results in a significant permeability increase at a distance of several slot diameters and dramatic reduction of the near wellbore conversion pressure drop. In gas wells it will reduce (or completely eliminate) sometimes very large non-darcy skin.
In order to optimize the method, the partial Abrasive Hydrojet Perforation is performed by cutting slots only in a surrounding column, cement layer and a part of the productive zones of the fromation.
This method allows cutting slots in a thin productive zone and in the case when the productive layer is not far away from water horizons. Abrasive Hydrojet Perforation is preformed by fluids, which includes water and quartz sand. This allows preserving the integrity of cement and leads toward higher penetration into the formation compared to other technology and methods (conventional perforation, hydrofracturing).
The technology can be divided into surface and underground equipment (FIG. 2). Underground equipment includes an engine with nozzles, which is connected to surface pumping units (FIG. 3). For Abrasive Hydrojet Perforation, hydrojet perforators (11) are used; for single slotting the perforator is used with 4 nozzles. Nozzles are located 180 degrees across from each other. The distance between nozzles is around 4xe2x80x3. The abrasive fluid is recycled all of the time during the process. In addition underground equipment includes (FIG. 3): underground engine (8), engine switch (9) and hydrojet perforator (11). This equipment can slot in one session three intervals with the approximate length of 3 ft. each. After that perforators must be changed. Description of the slotting technique is shown on (FIG. 4).
Surface equipment includes (FIG. 2) pumping units, mixer blender for sand/water, block manifold, filters and connectors. Pumping units for Abrasive Hydrojet Perforation can be used with the following characteristic: 5,00-10,000 psi, depending on well depth, and continuous working capacity of 6 hours.
Abrasive fluids prepared in blender. Filters are used to filter fluids and separate water for the recycling process. Quartz sand can be used as the abrasive material with quartz consumption not less then 50%.
During the Abrasive Hydrojet Perforation it is preferable preliminarily to determine the porosity and permeability of the production formation of the near wellbore zone, and the depth of the zone of support stresses, and to perform the subsequent treatment in dependence on the porosity and depth.
In particular, when the rock has a porosity of approximately 15% and higher, the Abrasive Hydrojet Perforation is performed at the depth of 1-1.5 well diameters, with the porosity of less than approximately 15% the Abrasive Hydrojet Perforation is performed at the depth not less than four well diameters.
In the first case, this reduces the time and cost of treatment almost in half, and in second case it guarantees achieving of the maximum possible effect. Moreover, during a subsequent cyclic treatment with technological reagents in order to increase permeability of the zone of remaining support stresses, between each treatment a radius of a zone of support pressure and a maximum acting stress in it are determined and the treatment is performed on a part of the formation which adjoins the well, including a zone of the support pressure. After each cycle of treatment, a change of density (permeability) of the formation in the zone of support pressure is controlled.
In order to optimize the method, the treatment is stopped when the density of the formation in the zone of support pressure is reduced by a predetermined value, which is determined in accordance with the formula:
xcex94xcfx81xe2x89xa7Kxcfx81("sgr"yxe2x88x92xcex3xc2x7H)/E, 
wherein K is a factor of efficiency of treatment,
xcfx81 is the density of the formation of a not disturbed formation at the depth, lb/ft3 
"sgr" is the maximum stress acting in the zone of support pressure MPa,
xcex3 is the specific weight of rock of the formation, lb/ft3,
E is an elasticity modules of formation rock, MPa.
It is also proposed in accordance with the present invention to use a technological solution with an acid reaction of flow, which interacts with a clay component of colmatating portions and a matrix of rock of a productive formation, whose composition is selected in accordance with the nature of the rock of the productive formation of a near well zone.
In particular, with a terrigen collector of the productive formation, the technological solution is a solution of NaHSO4xc3x97H2O and/or K2S2O7 and/or (NH)4S7O6 with concentration of 4-7%, with additions of anion active surface active substances or mixture of anion active and noionogenic surface active substances within the concentrations 0.5-2%.
If in a terrign collector, there is a carbonate component more than 30% and if there is a carbonated collector of the productive formation, the technological solution can be a solution of NH2SO4H with addition of anion active surface active substances or a mixture of anion active and non ionogenic surface active substances within the concentrations 02-04% and polyphosphates within the concentration 0.1-0.2% or a solution of CH3COCl with concentration 6-12% with admixtures of anion active surface active substances or a mixture of anion active and non ionogenic surface active substances within the concentration 0.5-1% or polyphosphates within the concentrations of 0.1-0.2% and as polyphosphates, there are used in Na5P3O10 and/or Na2[Na4(PO3)6].
In accordance with a further advantageous feature of the present invention, the formation treatment fluid (technological solution) is formed directly in a well within an interval of a formation to be treated, for example by enclosing of chemical agents for preparation of a solution into a transport package, transporting the package to the formation to be treated, and then removing the package for example by its dissolution with a solution in the well or by supplying of a dissolving liquid.
The transporting package can be formed as a micro container or capsule with a dissolvable enclosure formed, for example as a water soluble polyethylene film. The container can be also composed of a binding material, for example starch which is water soluble without the residues and consequences. Containers can be formed as balls or cylinders.
Thus, the new features of the present invention include a combination of operations, such as performance of the method in two stages with a primary controlled partial Abrasive Hydrojet Perforation and a subsequent controlled and regulated cyclical treatment of a well with a formation-treating agent, cutting of slots only in a surrounding column, a cement layer and a part of the rock of the collector immediately adjoining the well, preliminary determination of porosity of the rocks of the productive formation of the near well zone and a depth of a zone of support stress, and correction of a further treatment depending on the porosity and depth, determination of a radius of zone of support pressure and a maximum acting stress in it before each cycle of the formation treatment, carrying out of the treatment of all parts of the adjoining formation to the well including a zone of support pressure, controlling of a change of density (permeability, porosity) of rocks in the zone of support pressure after each treatment, stopping of the cyclical treatment when density of the formation in the zone of support pressure is reduced by a predetermined value, change of volumes (radii) of a mass which is treated in stages, selection of compositions of technological solutions and their preparation directly in a well in an interval of a treating formation. These features provide an unexpected result, which is a significant reduction of labor consumption and cost of the method without a reduction of efficiency of treatment and long-term stabilization of the obtained effects. These results are unobvious and inventive.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.